Pyrotechnical devices and methods of making the same



HIELLERN Feb. 4, 1964 PYROTECHNICAL DEVICES AND METHODS OF MAKING THESAME 3 Sheets-Sheet 1 Filed April 22, 1960 FIG. 2

FIG. 3

IN V EN TOR.

HERBERT ELLERN ATTORNEY 4 8 J, o 2 JW 3% w T m I K W F 0 N m R v m ET umm S E C I V E D L A C I N H C E T m 4Y 6 9 1 4" h e F 3 Sheets-Sheet 2Filed April 22, 1960 2 8 INVENTOR.

HERBERT ELLERN 6 FIG. 7

H. ELLERN Feb. 4, 1964 PYROTECHNICAL DEVICES AND METHODS OF MAKING THESAME 3 Sheets-Sheet 3 Filed April 22, 1960 FIG.9

FIG.||

IN V EN TOR. HERBERT ELLERN ATTORNEY United States Patent Office3,l2,l8l Fatented Felt. 4, 19%4 3,120,184 PYROTECEHJICAL DEVICE ANDMETHODS F MAKING THE SAME Herbert Ellern, Ferguson, Mo, assignor toUniversal Match Corporation, Ferguson, Mo, a corporation of DelawareFiled Apr. 22, 196%, Ser. No. 24,063 11 Claims. ((Il. lll237.8)

This invention relates in general to certain new and useful improvementsin pyrotechnical devices and methods of making the same and, moreparticularly, to pyrotechnical materials in which the incandescentexothermic reaction, once initiated, will proceed linearly in aprescribed direction at a constant rate and under preservation ofconstant area.

Many pyrotechnical devices and solid propellant grains, when ignited,will burn over all, or a substantial portion, of the surface area of thegrain is a somewhat predictable pattern and, as the grain is consumed,the area of burning surface will change. This type of burning isfrequently undesirable because of the shortness of time and sometimeserratic progression of the reaction. As a matter of fact, it isfrequently desirable to arrange a pyrotechnical reaction in such amanner that the incandescent exothermic reaction or burning, as it isusually called, will take place across a known area of the material andthat the burning will proceed linearly along the longest axis of thematerial while the area of burning remains constant. In this manner, itis possible to achieve very precise rates of burning and uniformproduction of pyrotechnically gen erated forces, such as gas-production,light-output, heat output, and the like.

In some cases, it is also desirable to provide a pyrotechnical device inwhich the reacting mass will burn from the central core outwardly whilethe external surfaces of the material are protected from burning, sothat the pyrotechnical reaction will proceed at an accelerated rate fromthe internally exposed surface because of constant increase in burningarea from the inside outwardly.

In all such cases, where the spread of the flame or glow front over asurface is to be avoided, efforts are usually made to inhibit thesurface. For instance, a loose powder-mixture may be pressed into a tubemade of some pyrotechnically inert material, such as cardboard, metal,or the like. Another method of surface inhibition which has beencommonly employed is to wrap pre-manufactured grains in a sheet ofsuitable material. Unfortunately, the existing methods involve bondsbetween the pyrotechnical surface and the inhibiting material which donot stand up under mechanical stresses, vibration, or extreme changes intemperature. Since pyrotechnical materials of the type here underdiscussion are quite often subjected to extremes of mechanical stressand vibration as well as extremes of temperature change, conventionalbonds frequently separate partially and cause increased burning rate ofan erratic nature starting at the exposed surface or crevice Where thebond has broken away. It is a common experience in rocket motors as wellas in flare candles and related devices that crevices of this type canbecome sufiiciently large to cause accelerated burning reachingexplosive proportions.

Furthermore, the conventional methods of inhibition have numeroustechnical and economical drawbacks. In the case of pyrotechnical items,the pressing of the ingredients into a structural part requires often acomplex and costly split mold-design. Pressing into the final structuralcomponents has other disadvantages, especially when pressing in severalincrements is necessary, such as difficult quality control because ofinaccessibility of the compressed material.

It is, therefore, the primary object of the present invention to providea surface-inhibited pyrotechnical material in which thesurface-inhibition is entirely reliable and will not break away from theinhibited surface or otherwise expose such surface to erratic burning.

It is another object of the present invention to provide means andmethods for reliably inhibiting the surface of pyrotechnical materialsso as to establish precisely predetermined burning rates and reactioncharacteristics.

With the above and other objects in view, my invention resides in thenovel features of form, construction, arrangement, and combination ofparts presently described and pointed out in the claims.

In the accompanying drawings (three sheets)- FIG. 1 is a perspectiveview of a pyrotechnical device constructed in accordance with andembodying the present invention;

FIG. 2 is a vertical sectional view taken along line 2-2 of FIG. 1;

FIGS. 3 and 4 are transverse sectional views taken along lines 3-3 and4-4, respectively, of FIG. 2;

FIGS. 5, 6, 7, and 8 are schematic views, some of which are in section,illustrating the method or process of manufacturing pyrotechnicaldevices according to the present invention;

FIG. 9 is a perspective view of a modified form of pyrotechnical deviceconstructed in accordance with and embodying the present invention;

MG. 10 is a perspective view of the pyrotechnical charge forming a partof the device shown in FIG. 9; and

FIG. 11 is a longitudinal sectional view taken along line llll of FIG.9.

Broadly speaking, the present invention relates to a method ofinhibiting the external surfaces of pyrotechnical masses, such as, forexample, cylindrical flare candles or cylindrical propellant powdergrains, by coating the surfaces, on which burning is to be precluded,with a soft, homogeneous, semi-solid material of high consistency and ofsuch physical character that within a wide range of temperatures neitherliquefaction nor solidification of the semi-solid material takes placMaterials which have been used and found satisfactory in connec tionwith the present invention are, for example, temperature resistantgreases, and plastomeric materials, such as semi-solid silicone polymerswhich evidence very slight viscosity change over wide ranges oftemperature variation. In this connection, it has been found that themost useful and satisfactory semi-solid materials, for purposes of thepresent invention, are the chemical compounds known as silicone oils,otherwise usually referred to as organo-poly-siloxanes, which areconverted, by addition of very finely ground mechanical thickeningagents, such as silica aerogel, or chemical agents such as lithiums'tearate, into stiff greases which do not change their semi-solid stateat temperatures as low as l00 F. or as high as +300 F. Theorgano-siloxanes which are operative in the present invention are setforth in Table 9 on page 184 of Chemistry of the Silicones (SecondEdition), Eugene G. Rochow, John Wiley & Sons, Inc, and discussed inChapter 6 thereof. Silicone greases which have been found to be suitablein the present invention are also described in US. Patents Nos.2,258,219, 2,258,- 222, 2,352,974, 2,371,068, 2,428,608, and 2,446,177.

Referring now in more detail and by reference characters to thedrawings, which illustrate a practical embodiment of the presentinvention and the method of making same, A designates a pyrotechnicaldevice consisting of an external canister 1, preferably, though notnecessarily, of a cylindrical shape, and formed of metal, cardboard, orother suitable rigid material, which is noncombustible, or does notburn, melt or disintegrate at a faster rate than the burning flarecandle recedes. The canister 1 is preferably provided with a flatintegral bottom wall 2. Disposed entirely within the canister 1 and ofsmaller diametrical and axial size with respect thereto is apyrotechnical material, such as a magnesium/oxidizer/binder flare candle3, which is held in concentric spaced relation internally of thecanister 1 by means of a plurality of short very small-diameter metallicpins 4, the latter being secured axially upon the outer surface of thecandle 3 by means of short sections of pressure-sensitive tape 5. Aswill be noted by reference to FIGS. 2, 3 and 4, two axially spaced setsof pins 4 are preferably employed and are located at 120 intervalsaround the surface of the candle 3, thereby insuring a relativelyuniform annular space between the interior face of the canister 1 andthe exterior surface of the candle 3. Since the candle 3 is somewhatshorter in length than the canister l, the space will extendtransversely between the bottom face of the candle 3 and the bottom wall2 of the canister 1. This space is completely filled with a semi-solidmaterial 6 of the type above stated.

Compressed into and forming the top layer of the candle f; is aconventional first-fire portion 7 which is annularly encircled with arubber or neoprene O-ring 3, the latter being held in place by a gasketring 9. Finally, the upper margin of the canister 1 is annularly crimpedover in the usual manner to form a sealing bead 10 which holds thegasket ring 9 in place.

As schematically illustrated in FIGS. to 8, inclusive, the pyrotechnicaldevice A is preferably manufactured in the following manner. Thecanister l is filled to a predetermined level with a quantity ofsemi-solid material 6. Meanwhile, the compressed candle 3 is providedaround its outer surface with a series of pins 4 held in place bysections of pressure-sensitive tape 5, as above described. The candle 3is then pushed firmly down into the canister It. In this condition, itshould be noted that the quantity of semi-solid material is computedrather accurately to correspond to the displacement of the candle 3, sothat when the latter is finally pushed down into place, the semisolidmaterial will rise upwardly in the canister 1 to precisely fill theentire space between the inner surface of. the canister l and the outersurface of the candle 3, with just enough clearance at the top to permitinsertion of the O-ring 8. Finally, the gasket ring 9 is inserted andpressed down on the O-ring 8 until it is flush with the top surface ofthe first-fire portion 7. As this is done, the O-ring 8 may tend to pushthe semi-solid material 6 back down into the cannister 1 to a slightdegree but a slight amount of a hydraulic compensation automaticallytakes place. In other words, the candle 3 may ease back upwardly a fewthousandths of an inch as the bead 10 is crimped over.

A pyrotechnical device thus designed will burn in a perfectly linearmanner and with a precisely reproducible burning rate. Moreover, such adevice will not alter its properties and will not burn erratically orexplosively when exposed to numerous cycles of extreme temperasurevariation on such as the frequently required cycle between -65 F. and+160 F. It will also retain its full inhibition bond on exposure torough handling and prolonged vibration because of the cushioning effectof the semi-solid envelope around the candle. In addition, the danger ofviolent reaction because of accidental cracks in the pellet surface ismuch reduced because of the sealant character of the inhibitor.

On burning, the inhibiting compound evaporates or burns away at the rateflare candle burns down, depending on the reaction temperature andthickness of inhibitor which will usually be no less than 0.005 inch orno more than 0.125 inch thick. Because of its low heat conductivity, itremains in place in the unburned part of the flare.

Essentially, the same arrangement as outlined above can be achieved byembedding solid rocket-propellant grains in silicone-grease compounds inorder to obtain linearly progressive end-burning or inside-to-outsideburning in perforated mechanically top-end inhibited grains. Thisafifords a simple means of slowing down the burning rate of propellantsfor rocketry or when used as gasgenerators for pressurization, for workin gas-turbines and similar one-shot items where close control andgradual developement of gas is of importance.

While the inhibition of burning achieved with compounds based onsilicone oils permits a particularly wide range of ambient temperatureexposure, it should be noted that for many purposes other highconsistency and more or less viscous, semi-solid, pasty chemicalcompounds or mixtures of chemical compounds can be employed as e.g.solid lubricants, petrolatum or highly plasticized lacquer bases with orwithout addition of chemical or mechanical thickeners.

Since pyrotechnical and some propellant mixtures are more or lessporous, a need may arise to seal the surface pores of the compressedmasses with a sealer which is impervious to any oily component of theinhibitor which may exude and gradually infiltrate by capillary actioninto the active material. Such protection will only be necessary if oneor more of the following adverse conditions prevail: high porosity ofthe flare candle; tendency of the inhibitor to release low viscosityoil; and prolonged exposure to elevated temperature which may promoteinfiltration. I have found that an excellent sealant for pyrotechnicalflare-candles is a very thin coat of shellac, but other lacquers orvarnishes may be used and need be applied only sparingly in a manner toseal the pores within the surface area without leaving a substantialfilm.

Another application of the present invention is shown in F165. 9 and 10which illustrate a modified form of pyrotechnical device B comprising anelongated canister or outer shell lll substantially similar to thepreviously described canister 1. The pyrotechnical charge 12, however,consists of a plurality of elongated compressed pyro; technical pellets13 which are assembled and held in endto-end relation by narrowencircling strips of adhesive tape 14 or by some similar mechanicalmeans. The assembled charge 12 is placed in the canister 1-1 andsurrounded by a semi-solid inhibitor mass 15 in the same manner aspreviously described in connection with the pyrotechnical device A.

While my invention has been described as suitable for flares andpropellant grains, it is applicable to any relatively slowlyexothermically reacting, solid mixture of chemicals or anyexothermically decomposing compound or compounds such as used for whiteand colored smokes, gas-cartridges as power sources, specificgas-producing mixtures, pyrochemical whistles, igniters and otherheatsources. It should also be noted that pyrotechnical devices, such asthe flarecandle above described, need not be cylindrical in shape, andit is also possible to use other very small mechanical spacing elementswhich will hold the pyrotechnical pellet in spaced relation within thecanister without materially interfering with the upward flow ofsemi-solid inhibition material.

It should be understood that changes and modifications in the form,construction, arrangement, and combination of the several parts of thepyrotechnical device and in the steps of its production may be made andsubstituted for those herein shown and described without departing fromthe nature and principle of my invention.

Having thus described my invention, What I claim and desire to secure byLetters Patent is:

1. A pyrotechnical device comprising an external canister of generallytubular shape, said canister having a closed bottom wall and acontinuous side wall, a solid pyrotechnical mass which is substantiallysimilar in geometrical shape to the interior of the canister and beingsmaller in cross-sectional dimension than the corresponding insidecross-sectional dimension of the canister by an amount in the range of0.005 to 0.125 inch in all lateral directions whereby to provide anannular space between the side wall of the canister and thepyrotechnical mass, said annular space having a width which issubstantially uniform and is in the range of 0.005 to 0.125 inch, saidpyrotechnical mass also having a bottom surface proximate to the bottomwall of the canister and disposed in spaced relation thereto, and asemi-solid non-pyrotechnical material disposed between the canister andthe pyrotechnical mass, said semi-solid non-pyrotechnical material beingonly in contact with the bottom wall and cylindrical side wall of saidmass.

52.. A pyrotechnical device comprising an external canister, ofgenerally tubular shape, said canister having a closed bottom wall and acontinuous side wall, a solid pyrotechnical mass which is substantiallysimilar in geometrical shape to the interior of the canister and beingsmaller in cross-sectional dimension than the corresponding insidecross-sectional dimension of the canister by an amount in the range of0.005 to 0.125 inch in all lateral directions whereby to provide anannular space between the side wall of the canister and thepyrotechnical mass, said annular space having a width which issubstantially uniform and is in the range of 0.005 to 0.125 inch, saidpyrotechnical mass also having a bottom surface proximate to the bottomwall of the canister and disposed in spaced relation thereto, a siliconegrease disposed between the canister and the pyrotechnical mass, andsealing means within said canister for preventing the top wall of saidmass from coming into contact with said silicone grease.

13. A pyrotechnical device comprising an external canister of generallycylindrical shape, said canister having a closed bottom wall and anannular side wall, a generally cylindrical solid pyrotechnical mass of adiameter which is smaller than the inside diameter of the canister by anamount which is in the range of 0.01 to .25 inch whereby to provide anannular space between the side wall of the canister and thepyrotechnical mass, said annular space having a width which issubstantially uniform and is in the range of 0.005 to 0.125 inch, saidpyrotechnical mass also having a bottom surface proximate to the bottomwall of the canister and disposed in spaced relation thereto, anorgano-polysiloxane disposed between the canister and the pyrotechnicalmass, and sealing means within said canister for preventing the top wallof said mass from coming into contact with said organo-poly-siloxane.

4. A pyrotechnical device comprising an external canister, apyrotechnical mass disposed within the canister in spaced relationthereto, and a surface inhibiting agent consisting of a methyl siliconeoil stiffened with a metal stearate disposed between the canister andthe pyrotechnical mass forming a thin film between said mass andcanister, said mass being completely enclosed within said film.

5. A pyrotechnical device comprising an external canister of generallycylindrical shape, said canister having a closed bottom wall and anannular side wall, a generally cylindrical solid pyrotechnical mass of adiameter which is smaller than the inside diameter of the can-ister byan amount which is in the range of 0.01 to 0.25 inch where by to providean annular space between the side wall of the canister and thepyrotechnical mass, said annular space having a width which issubstantially uniform and is in the range of 0.005 to 0.125 inch, saidpyrotechnical mass also having a bottom surface proximate to the bottomwall of the canister and disposed in spaced relation thereto, and asurface inhibiting agent consisting of a methyl silicone oil stiffenedwith lithium stearate disposed between the canister and thepyrotechnical mass, said inhibiting agent having a relatively constantviscosity in the temperature range of 65 F. to +160 F. and being in asemi-liquid state in such temperature range.

6. A linearly burning pyrotechnical device comprising a pyrotechnicalmass halving selected surfaces inhibited by a coating consisting of amethyl silicone oil stiffened with a metal stearate said metal stearateand methyl silicone oil combination being capable of maintaining arelatively constant viscosity between a temperature range of 65 F. and+160 F. and being in a semi-solid state in such temperature range.

7. A linearly burning pyrotechnical device comprising a pyrotechnicalmass having selected surfaces inhibited by a coating consisting of amethyl silicone oil stiffened with lithium stearate, said metal stearateand methyl silicone 'oil combination being capable of maintaining arelatively constant viscosity between a temperature range of 65 F. and+160 F. and being in a semi-solid state in such temperature range.

8. A linearly burning pyrotechnical device comprising a pyrotechnicalmass consisting of a plurality of elongated pyrotechnical pellets heldin end-to-end alignment by sections of adhesive tape which extendannularly around and entirely cover each of the abutting margins, saidpyrotechnical pellets having selected surfaces inhibited by a coatingconsisting of an organo-poly-siloxane.

9. A pyrotechnical device comprising an external canister, apyrotechnical mass having a top wall and -a bottom wall which merge intoa cylindrical side wall, said mass being disposed within the canister inspaced relation thereto, two sets of axially spaced pins mounted atdegree intervals on the surface of said mass, thereby providing uniformspacing between said mass and canister, said pins having a comparativelysmall length relative to the length of said mass, and anorgano-poly-siloxane disposed between the canister and the pyrotechnicalmass, said organo-poly siloxane being only in contact with the bottomwall and cylindrical side wall of said mass.

10. A pyrotechnical device comprising an external canister, apyrotechnical mass disposed within the canister in spaced relationthereto, and a methyl silicone oil stiffened with a metal stearatedisposed between the canister and the pyrotechnical mass forming a thinfilm between said mass and canister, said metal stearate and methylsilicone oil combination being capable of maintaining a relativelyconstant viscosity between a temperature range of -65 F. and +l60 F. andbeing in a semi-solid state in such temperature range.

11. A pyrotechnical device comprising an external canister, apyrotechnical mass disposed within the canister in spaced relationthereto, and a methyl silicone oil stiffened with a very finely groundmechanical thickening agent disposed between the canister and thepyrotechnical mass forming a thin film between said mass and canister,said mass being completely enclosed within said film, said film having athickness of not less than 0.005 inch and not more than 0.125 inch.

References (Jilted in the file of this patent UNITED STATES PATENTS958,990 Bourdelles May 24, 1910 1,187,779 Pattern June 20, 19161,785,529 Pratt Dec. 16, 1930 2,263,585 Moore et a1 Nov. 25, 19412,446,177 Hain June 21, 1945 2,455,242 =DWyer Nov. 30, 1948 2,479,828Geckler Aug. 23, 1949 2,541,334 Carey et a1. Feb. 13, 1951 2,543,079Veek Feb. 27, 1951 2,845,833 Davidson et a1. Aug. 5, 1958 2,877,504 FoxMar. 17, 1959 2,877,709 Duckworth Mar. 17, 1959 2,986,001 Green May 30,1961 3,054,253 Chung Sept. 18, 1962

1. A PYROTECHICAL DEVICE COMPRISING AN EXTERNAL CANISTER OF GENERALLY TUBULAR SHAPE, SAID CANISTER HAVING A CLOSED BOTTOM WALL AND A CONTINUOUS SIDE WALL, A SOLID PYROTECHNICAL MASS WHICH IS SUBSTANTIALLY SIMILAR IN GEOMETRICAL SHAPE TO THE INTERIOR OF THE CANISTER AND BEING SMALLER IN CROSS-SECTIONAL DIMENSION THAN THE CORRESPONDING INSIDE CROSS-SECTIONAL DIMENSION OF THE CANISTER BY AN AMOUNT IN THE RANGE OF 0.005 TO 0.125 INCH IN ALL LATERAL DIRECTIONS WHEREBY TO PROVIDE AN ANNULAR SPACE BETWEEN THE SIDE WALL OF THE CANISTER AND THE PYROTECHNICAL MASS, SAID ANNULAR SPACE HAVING A WIDTH WHICH IS SUBSTANTIALLY UNIFORM AND IS IN THE RANGE OF 0.005 TO 0.125 INCH, SAID PYROTECHNICAL MASS ALSO HAVING A BOTTOM SURFACE PROXIMATE TO THE BOTTOM WALL OF THE CANISTER AND DISPOSED IN MATERIAL DISPOSED BETWEEN THE CANISTER AND THE PYROTECHNICAL MASS, SAID SEMI-SOLID NON-PYROTECHNICAL MATERIAL BEING ONLY IN CONTACT WITH THE BOTTOM WALL AND CYLINDRICAL SIDE WALL OF SAID MASS. 